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I'm having difficult understanding the output after running the zpool status command:

    NAME        STATE     READ WRITE CKSUM
    tank        ONLINE       6     0     0
      raidz2-0  ONLINE       0     0     0
        c3t0d0  ONLINE       0     0     0
        c3t1d0  ONLINE       0     0     0
        c3t2d0  ONLINE       0     0     0
        c3t3d0  ONLINE       0     0     0

I see a 6 next to READ, which I assume are I/O errors trying to read from tank. What I don't understand is which drive is at fault here to replace. Is this something to be alarmed about? I ran a SMART test and none of the drives reported a fault. I'm not exactly sure how to handle this problem.

2 Answers 2

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Please run:

zpool scrub tank

And then look a little more into the properties and attitudes of ZFS and how it tries to protect data.

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    more context ( from docs.oracle.com/cd/E19253-01/819-5461/gbbxi/index.html ): "The simplest way to check data integrity is to initiate an explicit scrubbing of all data within the pool. This operation traverses all the data in the pool once and verifies that all blocks can be read. Scrubbing proceeds as fast as the devices allow, though the priority of any I/O remains below that of normal operations. This operation might negatively impact performance, though the pool's data should remain usable and nearly as responsive while the scrubbing occurs." Follow it with zpool status -v tank Jan 2, 2015 at 8:46
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Reported errors do not necessarily mean the drive is failing. A sector may have just gone bad and been replaced from the reserve pool. ZFS will automatically repair any corrupted data with good data from the other drives.

If the number of errors keeps increasing however that means more sectors are going bad and is a sure sign of a drive about to fail. Continue to do smart selftests (long) and zpool scrub over the next several days. If you don't see more errors the drive is probably ok for now.

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